Amylase (enzyme number: EC3.2.1.1) is secreted from pancreas, salivary gland and so on, and is mostly distributed in salivary gland and pancreas. Besides those, it is known to be present in muscle, ovary and oviduct as well. It is further known that amylase which is exuded from tissues is present in blood and urine. It is known that amylase value in serum, urine or pancreatic juice shows a high value in a part of functional disorders of pancreas or salivary gland and kidney or liver, or neoplastic disease. With regard to a method for measuring such amylase activity, there have been already known a Caraway method or an enzymatic method using an oligosaccharide substrate, etc. All of those methods are able to measure amylase activity to an extent of thousands IU/L and have been used for the measurement of serum, pancreatic juice, urine sample, etc. in which the normal value of amylase activity is from about tens to hundreds IU/L.
According to the studies in recent years, it has been reported that saliva amylase activity value is correlated to stress of a subject [Japanese journal of medical electronics and biological engineering, 39(3), p. 234–239 (2001), Masaki Yamaguchi, et al.], and a method for measuring amylase activity value in saliva samples has been demanded.
However, normal value of amylase activity in saliva is several ten thousands IU/L, so that it is unable to directly measure amylase activity in saliva by the conventional method. Accordingly, extra operations such as dilution of a sample are necessary and, in addition, dilution to an extent of several hundred times is necessary whereby there is a problem of causing a decrease in the precision of the measurement.